Investigation on the hydriding/dehydriding properties of Mg₉₅Ni₅-30wt%La_0.7Mg_0.3 Ni_2.8Co_0.5 composite

Mg₉₅Ni₅ was prepared by hydriding combustion synthesis (HCS) from the powder mixtures of Mg and Ni, and then the HCS product together with 30wt% La_0.7Mg_0.3Ni_2.8Co_0.5 alloy were subjected to mechanical milling for 5, 10, 15 and 20 h, respectively. The HCS product was also milled for 10 h for comparison. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX) and gas reaction controller, the phase structure, microstructure and hydriding/dehydriding properties of the composites were studied in detail. It was found the composite milled for 10 h had the best hydriding/dehydriding properties. It required only 50 s to absorb its saturated hydrogen capacity of 3.78wt% at 373 K and desorbed 3.83wt% hydrogen within 1800 s at 523 K. Moreover, the dehydriding temperature onset of the composite was 425 K, which was 35 K lower than that of Mg₉₅Ni₅. The improved hydriding/dehydriding properties were related greatly with the structures of the composites, and the addition of La_0.7Mg_0.3Ni_2.8Co_0.5 could improve the dehydriding kinetics of the composites.